Science: Navigation in Space

The most optimistic talk about space travel comes from the engineers who
design the rocketships for the future. All they need for a trip to the moon, they
say, is sufficient funds ($4 billion) and an all-out engineering effort like the one
that produced the Abomb. To British Astronomer J. G. Porter, writing in the
scientific monthly Discovery, "some element of doubt creeps in."
His engineering brethren, he says, have overlooked some basic difficulties
obvious to any stargazer.

Bucket on a String. The general idea of space travel, Porter concedes,
is "sound enough." Using...